The fuel cell transforms a chemical energy of a fuel into an electric energy by means of a chemical reaction, directly. Different from a related art battery, the fuel cell can generate electricity continuously without recharge as far as the fuel is supplied. Owing to the high energy efficiency, and the environment friendly nature, interest is focused thereto, recently.
In general, the fuel cell has two electrodes, i.e., an anode and a cathode arranged on both sides of an electrolyte. There are an anode side separator at an outer side of the anode having a fuel passage for supporting the anode, and a cathode separator at an outer side of the cathode having an air passage for supporting the cathode. Electro-chemical reaction of hydrogen takes place at the anode, and electrochemical reduction of oxygen, an oxidizer, takes place at the cathode, when an electric energy is generated as electrons generated in this time transfer.
A variety of fuels in a hydrocarbon group (CH group), such as LNG, LPG, methanol, gasoline, and the like can be used in the fuel cell. In general, the fuel is refined into hydrogen through desulfurization, reforming reaction, and hydrogen refining process at a fuel reformer, and used in a form of a gas. Or, a fuel in a form of water solution may be used, for an example, by making solid state BH−4 into a water solution state (Boro Hydro Fuel Cell:BFC). The BFC has an advantage in that no fuel reformer is required, which enables to simplify a fuel cell system, because a fuel of a water solution state is fed to the anode, and the reforming reaction takes place at the anode, without the fuel reformer.
In the meantime, in the fuel cells, there are a phosphoric fuel cell, a molten carbonate fuel cell, an alkaline fuel cell, a solid oxide fuel cell, and a polymer membrane fuel cell depending on electrolytes.
A related art fuel cell system will be described with reference to FIG. 1.
Referring to FIG. 1, the fuel stored in a fuel tank 5 is supplied to a fuel cell 1 by a fuel pump 3, and air is supplied to the fuel cell 1 by an air pump 7. The fuel cell 1 may be a unit cell or a stack of unit cells.
An exemplary related art fuel cell will be described with reference to FIGS. 2 and 3. FIG. 2, or 3 illustrates unit cell.
There are an anode 30 and a cathode 20 arranged on opposite sides of an electrolyte 10. There are separators 40 and 50 at outer sides of the anode 30 and the cathode 20. Both the anode 30 and the cathode 20 are porous and in general contain platinum.
As described, there are an anode side separator 50 at an outer side of the anode 30, and a cathode side separator 40 at an outer side of the cathode 20. The separators 40, and 50 support the anode 30 and the cathode 20, and have flow passages 46 and 56 formed with walls 44, and 54, respectively. There may be a variety of forms of the flow passages. The separator 40 or 50 also separates adjacent unit cells in a unit cell stack. Meanwhile, there may be separate collector plates at outer sides of the separators 40 and 50, respectively.
In general, the electrolyte 10, an ion exchange membrane of a polymer, such as NAFION® from DuPont™, transmits hydrogen ions, and prevents contact of oxygen and hydrogen. In general, the anode 30 and the cathode 20, supporters having catalyst attached thereto, are porous carbon paper, or carbon cloth. In general, the separators 40 and 50 are close textured carbon plates.
The operation of the fuel cell will be described.
The fuel and air supplied to the fuel cell flow through the anode 30 and the cathode 20 respectively, and make the following reactions.                Anode: BH4+80H BO2+6H2O+8e E0=−1.24V        Cathode: 2O2+4H2O+8e 80H E0=0.4V        Total: BH4+2O22H2O+BO2 E0=1.62V        
In the meantime, for stabilizing a BH4 solution, a certain amount of Na is added, to cause a side reaction at the anode 30 to generate hydrogen gas. That is, a reaction of 2H2O+NaBH4 NaBO2+4H2 takes place at the anode 30.
The related art fuel cell has the following problem.
The hydrogen gas generated by the side reaction at the anode is attached in forms of bubbles between the anode and the electrolyte to impede reaction between the fuel and the air, to result in a poor electricity generation performance.
In the meantime, the problem is caused in fuel cells other than the BFC, too. Because in general the side reaction takes place in cases hydrogen is not supplied to the anode directly as a fuel, resulting to have a substance produced in the side reaction attached between the electrolyte and the anode, to impede the chemical reaction. The substance produced in the side reaction may be, for an example, carbon dioxide other than the hydrogen gas depending on the fuel.